We propose a prototype authoring tool to synchronize among computer graphics animation, narration, and background music through the simple and interactive manipulation of a graphical interface. It is meant to be of assistance to those who lack special knowledge and/or skill in editing such media. The tool provides the following two features. First, users can visually grasp the contents of a background music track and a narration along a single timeline, and can also display the scenario of a computer graphics animation sharing the same timeline. Second, this tool provides a graphical user interface for interactively editing (reducing and/or expanding) both background music and narration without any deterioration. That is, the tool can synchronize the playback time of the background music with the corresponding portion of the computer graphics animation specified by the users by means of changing the tempo of all or a partial portion of the background music. According to the users' input parameters for editing (reducing or expanding), the tool also can automatically select and edit quasi-silent portions of the narration, thereby synchronizing the computer graphics animation and the narration.